The sun is in the currently in its quietest period for more than a century.

For the second time this month, Vencore Weather claims the sun has gone into 'cue ball' mode, with images from Nasa showing no large visible sunspots on its surface.

Astronomers say this isn't unusual, and solar activity waxes and wanes in 11-year cycles, and we're currently in Cycle 24, which began in 2008.

However, if the current trend continues, then the Earth could be headed for a 'mini ice age' researchers have warned.

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The sun is in the currently in its quietest period for more than a century. For the second time this month, the sun has gone into 'cue ball' mode, with images from Nasa showing no large visible sunspots on its surface

THE SOLAR CYCLE

Conventional wisdom holds that solar activity swings back and forth like a simple pendulum.

At one end of the cycle, there is a quiet time with few sunspots and flares.

At the other end, solar max brings high sunspot numbers and frequent solar storms.

It's a regular rhythm that repeats every 11 years.

Reality is more complicated.

Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular.

We've had the smallest number of sunspots in this cycle since Cycle 14, which reached its maximum in February of 1906.

On June 4th, the sun went completely spotless and activity remained low for around four days.

This follows another period of inactivity in February when another image of Nasa showed the sun in 'cueball mode'.

'The blank sun is a sign that the next solar minimum is approaching and there will be an increasing number of spotless days over the next few years,' wrote Vencore Weather.

During Solar Minimum, the opposite occurs. Solar flares are almost non-existent while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.

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The sun is in the midst of its quietest period in more than a century. In February, it was in 'cue ball' mode, with an incredible image from Nasa showing no large visible sunspots seen on its surface

THE MAUNDER MINIMUM

Maunder Minimum (also known as the prolonged sunspot minimum) is the name used for the period starting in about 1645 and continuing to about 1715 when sunspots became exceedingly rare, as noted by solar observers of the time

The Maunder Minimum (also known as the prolonged sunspot minimum) is the name used for the period starting in about 1645 and continuing to about 1715 when sunspots became exceedingly rare, as noted by solar observers of the time.

It caused London's River Thames to freeze over, and 'frost fairs' became popular.

This period of solar inactivity also corresponds to a climatic period called the 'Little Ice Age' when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes.

There is evidence that the Sun has had similar periods of inactivity in the more distant past, Nasa says.

The connection between solar activity and terrestrial climate is an area of on-going research.

Some scientists hypothesize that the dense wood used in Stradivarius instruments was caused by slow tree growth during the cooler period.

Instrument maker Antonio Stradivari was born a year before the start of the Maunder Minimum.

The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years.

During this period, sunspots were rarely observed and the solar cycle seemed to have broken down completely.

The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere.

Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.

A study last year claimed to have cracked predicting solar cycles - and says that between 2020 and 2030 solar cycles will cancel each other out.

This, they say, will lead to another 'Maunder minimum' - which has previously been known as a mini ice age when it hit between 1646 and 1715.

The model of the sun's solar cycle produced unprecedentedly accurate predictions of irregularities within the sun's 11-year heartbeat.

Show here is a plot of the monthly sunspot number so far for the current cycle (red line) compared to the mean solar cycle (blue line) and the similar solar cycle no. 5 (black)

The Frozen Thames, 1677 - an oil painting by Abraham Hondius shows the old London Bridge during the Maunder Minimum

It draws on dynamo effects in two layers of the sun, one close to the surface and one deep within its convection zone.

Predictions from the model suggest that solar activity will fall by 60 per cent during the 2030s to conditions last seen during the 'mini ice age' that began in 1645, according to the results presented by Professor Valentina Zharkova at the National Astronomy Meeting in Llandudno.

The model predicts that the pair of waves become increasingly offset during Cycle 25, which peaks in 2022.

During Cycle 26, which covers the decade from 2030-2040, the two waves will become exactly out of synch and this will cause a significant reduction in solar activity.

'In cycle 26, the two waves exactly mirror each other – peaking at the same time but in opposite hemispheres of the Sun,' said Zharkova.

'Their interaction will be disruptive, or they will nearly cancel each other.

'We predict that this will lead to the properties of a 'Maunder minimum'.

Montage of images of solar activity between August 1991 and September 2001 taken by the Yohkoh Soft X-ray Telecope, showing variation in solar activity during a sunspot cycle